"Men can unconsciously smell when a woman is ovulating."
According to a study published in Psychological Science, men are able to detect the scent of a fertile woman, even if they're unaware of what it is they're detecting. Researchers asked two groups of men to smell t-shirts. Some had been worn by women at various points in their menstrual cycles; others were unworn control-group shirts. Men who smelled the shirts of ovulating women experienced an increase in testosterone levels. Furthermore, they rated the shirts worn by ovulating women as the most pleasant-smelling.